Typically the refilling of storage vessels, particularly fuel tanks, involves the use of refuelling nozzles having automatic shut-off. The fuel tank is vented but designed so that pressure inside the tank increases as the tank is close to full. The refilling nozzle includes a pressure-sensitive mechanism which provides for automatic shut-off as the tank approaches its full level. The automatic shut-off nozzle is triggered by the pressure sensitive mechanism for closure at a preset pressure as the tank is close to full.
More recently it has been desirable to not pressurise the tank or vessel to be filled. In these applications such as refilling engine fuel tanks, there is still a requirement to prevent overfilling of the tank. This is achieved by automatic closure of a flow control valve associated with the tank and to which fluid couplings are connected to facilitate the refilling process. The flow control valve is designed to be closed when the tank is full as detected by a fluid level sensor. In a hydraulically controlled system, the fluid level sensor typically includes a float valve which closes when the tank is full. This closure of the float valve restricts or stops the flow of fluid bled from the flow control valve to effect its automatic closure. The patent literature is replete with refuelling systems of this nature such as U.S. Pat. No. 6,311,723 by Shipp & Turner.
The fluid level sensor such as that disclosed in U.S. Pat. No. 6,311,723 may include a float connected to the float valve via a float arm in a similar manner to a conventional toilet cistern or other cantilever style float valves. In more sophisticated systems, the float valve includes a cylindrical-shaped housing which contains a float which controls the actuation of an inlet valve to in turn hydraulically activate the flow control valve for closure when the tank has reached its nominated “full” capacity and prior to overfilling of the tank. The valve assembly disclosed in international patent application no. PCT/AU2003/001436 by Smit is an example of a float valve of this construction.
U.S. Pat. No. 4,305,422 by Bannink discloses a filler valve for a fuel tank, comprising a valve body to be mounted in the wall of the tank. The upper end of the valve body is where a filler hose can be connected. The wall of the valve body includes outlet ports and two shut-off valves are provided in the valve body. A passage is present between the shut off valves and the space between the two valves is in open communication with the space under the valve members. The space under the valve members includes a passage opening that is controlled by a float. When the tank approaches full, the float will shut an opening such that the pressure of liquid in the space under the second shut off valve and in the space between the two valves will become equal to the pump or filling pressure and as a result the valves will close.
U.S. Pat. No. 8,281,823 by Mitrovich discloses a refueling apparatus having a combination float control module and a fluid flow control valve for use in high pressure, high flow rate refueling systems. The fluid flow control valve includes a piston that includes a convex shaped head with beveled edges that is operable to open in response to the initiation of flow from a filler nozzle through the valve. The piston has a centrally located bleed passageway that provides fluid communication between opposite sides of the piston to thereby allow fluid to bleed via a bleed passage to the float control module. When the float control module detects the tank is full it shuts off the bleed passage to thereby change the relative pressures of liquid on opposite sides of the piston to thereby close the piston and shut off the flow of fluid.
In refilling storage vessels it is generally advantageous to provide maximum fluid flow to minimise the associated fill time. Existing fluid flow control valves are characterised by turbulence in the flow of the fluid through the valve assembly resulting in reduced flow rates and undesirable back pressure. Also, existing automatic shut-off nozzles have a tendency to prematurely shut-off at relatively high flowrates before the vessel has reached its “full” design capacity due to back pressure resulting from obstructions (“chokes”) to the flow of fluid through the flow control valve. In order to ensure complete filling of the vessel, operators may manually (or otherwise forcibly) override the automatic (pressure sensitive) shut-off mechanism of the nozzle increasing the risk of overfilling the vessel and causing fuel spillage with its associated hazards.